DESCRIPTION (adapted from the application) Energy metabolism plays an important role in body weight control and overall nutrition. Changes in energy expenditure (EE) can alter energy balance. Activity of the autonomic nervous system (ANS) influences daily EE. Previous studies have found associations between resting EE and some measures of ANS activities in certain populations. However, the quantitative roles of ANS activity in regulating other components of EE are unclear. In particular, the ANS regulation of physical activity and associated EE should be investigated since this component contributes the largest variation to daily EE. Some digestive diseases with altered energy metabolism, such as Cirrhosis, also have altered ANS activity, but the relationship between the regulatory mechanisms is unknown. Advances in technology and biomedical engineering can facilitate the accurate measurements of ANS activity, energy metabolism, and physical activity. We will utilize an unique combination of a whole-room indirect calorimetry chamber, a force platform floor, and a electronic activity sensing system to quantify the amount of EE and physical activity in a 24-hour period; multiple portable movement detectors and a novel force measurement insole device that we developed to accurately determine the type, intensity, duration, and frequency of the physical activities in 7 days of free living. We will obtain a comprehensive ANS activity profile includes multiple indices such as plasma catecholamines, urinary excretion of catecholamines, microneurography, and heart rate variability. Using these accurate measurements, we hope to establish quantitative associations between EE and ANS activity. We will explore the role of ANS plays in EE and physical activity in four groups of adult human subjects with various ANS activity levels: 1) a heterogeneous healthy normals, varying in age, gender, weight, and ethnicity, 2) patients with Pure Autonomic Failure who have very low ANS activities, 3) patients with Orthostatic Intolerance who have very high ANS activities, and 4) patients with cirrhosis who have various levels of ANS alterations. Results of this study should lead to improved understanding of ANS in controlling energy metabolism in normal and disease states. Experiences gained from this project and the didactic training will also help me to develop into an independent investigator in biomedical research.